title: A tumorigenic actin mutant alters fibroblast morphology and multicellular assembly properties.
abstract: Tumor initiation and progression are accompanied by complex changes in the cytoarchitecture that at the cellular level involve remodeling of the cytoskeleton. We report on the impact of a mutant β-actin (G245D-actin) on cell structure and multicellular assembly properties. To appreciate the effects of the Gly245Asp substitution on the organization of the actin cytoskeleton, we examined the polymerization properties of G245D-actin in vitro by pyrene polymerization assays and total internal reflection fluorescence microscopy (TIRF). The mutant actin on its own has a significantly reduced polymerization efficiency compared to native actin but also modifies the polymerization of actin in copolymerization experiments. Comparison of the structure of Rat-2 fibroblasts and a stably transfected derivate called Rat-2-sm9 revealed the effects of G245D-actin in a cellular environment. The overall actin levels in Rat-2-sm9 show a 1.6-fold increase with similar amounts of mutant and wild-type actin. G245D-actin expression renders Rat-2-sm9 cells highly tumorigenic in nude mice. In Rat-2-sm9 monolayers, G245D-actin triggers the formation of extensive membrane ruffles, which is a characteristic feature of many transformed cells. To approximate complex cell-cell and cell-matrix interactions that occur in tumors and might modulate the effects of G245D-actin, we extended our studies to scaffold-free 3D spheroid cultures. Bright field and scanning electron microscopy (SEM) show that Rat-2-sm9 and Rat-2 cells share essential features of spheroid formation and compaction. However, the resulting spheroids exhibit distinct phenotypes that differ mainly in surface structure and size. The systematic comparison of transformed and normal spheroids by SEM provides new insights into scaffold-free fibroblast spheroid formation.
authors.affiliation: Focal Area Structural Biology and Biophysics, Biozentrum, University of Basel, Basel, Switzerland.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Blache
authors.forename: Unai
authors.initials: U
authors.lastname: Silván
authors.forename: Marija
authors.initials: M
authors.lastname: Plodinec
authors.forename: Rosmarie
authors.initials: R
authors.lastname: Suetterlin
authors.forename: Roman
authors.initials: R
authors.lastname: Jakob
authors.forename: Ina
authors.initials: I
authors.lastname: Klebba
authors.forename: Mohamed
authors.initials: M
authors.lastname: Bentires-Alj
authors.forename: Ueli
authors.initials: U
authors.lastname: Aebi
authors.forename: Cora-Ann
authors.initials: CA
authors.lastname: Schoenenberger
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism; D000199:Actins / Q000378:metabolism*; D000818:Animals; D063646:Carcinogenesis / Q000378:metabolism / Q000473:pathology*; D049109:Cell Proliferation; D048430:Cell Shape; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology* / Q000648:ultrastructure; D051379:Mice; D008819:Mice, Nude; D050505:Mutant Proteins / Q000378:metabolism; D009154:Mutation / Q000235:genetics*; D058105:Polymerization; D011817:Rabbits; D051381:Rats; D018874:Spheroids, Cellular / Q000378:metabolism / Q000473:pathology* / Q000648:ultrastructure; D022502:Stress Fibers / Q000378:metabolism
chemical_list: D000199:Actins; D050505:Mutant Proteins
keywords: actin mutation; actin polymerization; membrane ruffling; multicellular spheroids; transformation; tumorigenic